U.S. patent application number 17/105071 was filed with the patent office on 2021-07-01 for all solid battery and manufacturing method of the same.
This patent application is currently assigned to TAIYO YUDEN CO., LTD.. The applicant listed for this patent is TAIYO YUDEN CO., LTD.. Invention is credited to Daigo ITO, Chie KAWAMURA, Takato SATO, Masashi SEKIGUCHI, Sachie TOMIZAWA.
Application Number | 20210202985 17/105071 |
Document ID | / |
Family ID | 1000005261695 |
Filed Date | 2021-07-01 |
United States Patent
Application |
20210202985 |
Kind Code |
A1 |
SATO; Takato ; et
al. |
July 1, 2021 |
ALL SOLID BATTERY AND MANUFACTURING METHOD OF THE SAME
Abstract
An all solid battery includes a solid electrolyte layer of which
a main component is a Li--Al-M-PO.sub.4-based phosphoric acid salt,
a first electrode layer that is provided on a first main face of
the solid electrolyte layer and includes an active material, and a
second electrode layer that is provided on a second main face of
the solid electrolyte layer and includes an active material. "M" is
at least one of Ge, Ti, and Zr. A region in which a ratio of
MO.sub.2 with respect to Li--Al-M-PO.sub.4 is 5% or more is
unevenly distributed from a center in a thickness of the solid
electrolyte layer to 0.4 A downward and to 0.4 A upward, when the
thickness of the solid electrolyte layer is expressed by "A".
Inventors: |
SATO; Takato; (Tokyo,
JP) ; ITO; Daigo; (Tokyo, JP) ; TOMIZAWA;
Sachie; (Tokyo, JP) ; KAWAMURA; Chie; (Tokyo,
JP) ; SEKIGUCHI; Masashi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIYO YUDEN CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
TAIYO YUDEN CO., LTD.
Tokyo
JP
|
Family ID: |
1000005261695 |
Appl. No.: |
17/105071 |
Filed: |
November 25, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/366 20130101;
H01M 10/0585 20130101; H01M 10/0562 20130101; H01M 10/0525
20130101 |
International
Class: |
H01M 10/0562 20060101
H01M010/0562; H01M 10/0585 20060101 H01M010/0585; H01M 10/0525
20060101 H01M010/0525; H01M 4/36 20060101 H01M004/36 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2019 |
JP |
2019-238340 |
Claims
1. An all solid battery comprising: a solid electrolyte layer of
which a main component is a Li--Al-M-PO.sub.4-based phosphoric acid
salt; a first electrode layer that is provided on a first main face
of the solid electrolyte layer and includes an active material; and
a second electrode layer that is provided on a second main face of
the solid electrolyte layer and includes an active material,
wherein "M" is at least one of Ge, Ti, and Zr, wherein a region in
which a ratio of MO.sub.2 with respect to Li--Al-M-PO.sub.4 is 5%
or more is unevenly distributed from a center in a thickness of the
solid electrolyte layer to 0.4 A downward and to 0.4 A upward, when
the thickness of the solid electrolyte layer is expressed by
"A".
2. The all solid battery as claimed in claim 1, wherein an average
crystal grain diameter of the MO.sub.2 is 0.2 .mu.m or more and 5
.mu.m or less in the solid electrolyte layer.
3. The all solid battery as claimed in claim 1, wherein "M" is
Ge.
4. A manufacturing method of an all solid battery comprising:
preparing a multilayer structure in which a paste for a first
electrode layer including an active material is provided on a first
main face of a green sheet including Li--Al-M-PO.sub.4-based
phosphoric acid salt powder, and a paste for a second electrode
layer including an active material is provided on a second main
face of the green sheet; and firing the multilayer structure,
wherein "M" is at least one of Ge, Ti and Zr, wherein a region in
which a ratio of MO.sub.2 with respect to Li--Al-M-PO.sub.4 is 5%
or more is unevenly distributed from a center in a thickness of a
solid electrolyte layer formed by firing the green sheet to 0.4 A
downward and to 0.4 A upward when the thickness of the solid
electrolyte layer is expressed by "A", by adding MO.sub.2 particles
in the green sheet and adjusting a condition of the firing.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2019-238340,
filed on Dec. 27, 2019, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] A certain aspect of the present invention relates to an all
solid battery and a manufacturing method of the all solid
battery.
BACKGROUND
[0003] High ionic conductivity can be achieved by using phosphoric
acid salt having a NASICON structure, as solid electrolyte layers
of an all solid battery. The phosphoric acid salt is such as
Li--Al-M-PO.sub.4-based phosphoric acid salt ("M" is such as Ge,
Ti, or Zr) (for example, see Japanese Patent Application
Publication No. 2018-73554).
SUMMARY OF THE INVENTION
[0004] However, in the solid electrolyte layers, MO.sub.2, an oxide
of "M", may diffuse into electrode layers. When MO.sub.2 diffuses
into the electrode layers, a composition of the
Li--Al-M-PO.sub.4-based phosphoric acid salt may fluctuate. And,
the high ionic conductivity may not be necessarily achieved.
MO.sub.2 does not ionic conductivity. When MO.sub.2 exists near
interfaces between the solid electrolyte layers and the electrode
layers because of the diffusion, the number of ion conduction paths
decreases. Therefore, the high ionic conductivity may not be
necessarily achieved.
[0005] According to an aspect of the present invention, there is
provided an all solid battery including: a solid electrolyte layer
of which a main component is a Li--Al-M-PO.sub.4-based phosphoric
acid salt; a first electrode layer that is provided on a first main
face of the solid electrolyte layer and includes an active
material; and a second electrode layer that is provided on a second
main face of the solid electrolyte layer and includes an active
material, wherein "M" is at least one of Ge, Ti, and Zr, wherein a
region in which a ratio of MO.sub.2 with respect to
Li--Al-M-PO.sub.4 is 5% or more is unevenly distributed from a
center in a thickness of the solid electrolyte layer to 0.4 A
downward and to 0.4 A upward, when the thickness of the solid
electrolyte layer is expressed by "A".
[0006] According to another aspect of the present invention, there
is provided a manufacturing method of an all solid battery
including: preparing a multilayer structure in which a paste for a
first electrode layer including an active material is provided on a
first main face of a green sheet including Li--Al-M-PO.sub.4-based
phosphoric acid salt powder, and a paste for a second electrode
layer including an active material is provided on a second main
face of the green sheet; and firing the multilayer structure,
wherein "M" is at least one of Ge, Ti and Zr, wherein a region in
which a ratio of MO.sub.2 with respect to Li--Al-M-PO.sub.4 is 5%
or more is unevenly distributed from a center in a thickness of a
solid electrolyte layer formed by firing the green sheet to 0.4 A
downward and to 0.4 A upward when the thickness of the solid
electrolyte layer is expressed by "A", by adding MO.sub.2 particles
in the green sheet and adjusting a condition of the firing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates a schematic cross section of a basic
structure of an all solid battery;
[0008] FIG. 2 illustrates a schematic cross section of another all
solid battery;
[0009] FIG. 3A to FIG. 3C illustrate cross sectional views of a
solid electrolyte layer, a first electrode layer adjacent to the
solid electrolyte layer and a second electrode layer adjacent to
the solid electrolyte layer;
[0010] FIG. 4 illustrates a measuring method of a MO.sub.2
segregation range;
[0011] FIG. 5 illustrates a flowchart of a manufacturing method of
an all solid battery; and
[0012] FIG. 6 illustrates a stacking process.
DETAILED DESCRIPTION
[0013] A description will be given of an embodiment with reference
to the accompanying drawings.
[0014] (Embodiment) FIG. 1 illustrates a schematic cross section of
a basic structure of an all solid battery 100 in accordance with an
embodiment. As illustrated in FIG. 1, the all solid battery 100 has
a structure in which a first internal electrode 10 and a second
internal electrode 20 sandwich a solid electrolyte layer 30. The
first internal electrode 10 is provided on a first main face of the
solid electrolyte layer 30. The first internal electrode 10 has a
structure in which a first internal electrode layer 11 and a first
electric collector layer 12 are stacked. The first internal
electrode layer 11 is on the solid electrolyte layer 30 side. The
second internal electrode 20 is provided on a second main face of
the solid electrolyte layer 30. The second internal electrode 20
has a structure in which a second internal electrode layer 21 and a
second electric collector layer 22 are stacked. The second internal
electrode layer 21 is on the solid electrolyte layer 30 side.
[0015] When the all solid battery 100 is used as a secondary
battery, one of the first internal electrode 10 and the second
internal electrode 20 is used as a positive electrode and the other
is used as a negative electrode. In the embodiment, as an example,
the first internal electrode 10 is used as a positive electrode,
and the second internal electrode 20 is used as a negative
electrode.
[0016] A main component of the solid electrolyte layer 30 is
phosphoric acid salt-based solid electrolyte having a NASICON
structure. The phosphoric acid salt-based solid electrolyte having
the NASICON structure has a high conductivity and is stable in
normal atmosphere. The phosphoric acid salt-based solid electrolyte
is, for example, such as a salt of phosphoric acid including
lithium. The phosphoric acid salt is not limited. For example, the
phosphoric acid salt is such as composite salt of phosphoric acid
with Ti (for example LiTi.sub.2(PO.sub.4).sub.3). In order to
increase an amount of Li, a part of Ti may be replaced with a
transition metal of which a valence is three, such as Al, Ga, In, Y
or La. In concrete, the phosphoric acid salt including lithium and
having the NASICON structure is
Li.sub.1+xAl.sub.xGe.sub.2-x(PO.sub.4).sub.3,
Li.sub.1+xAl.sub.xZr.sub.2-x(PO.sub.4).sub.3,
Li.sub.1+xAl.sub.xT.sub.2-x(PO.sub.4).sub.3 or the like. For
example, it is preferable that Li--Al--Ge--PO.sub.4-based material,
to which a transition metal included in the phosphoric acid salt
having the olivine type crystal structure included in the first
internal electrode layer 11 and the second internal electrode layer
21 is added in advance, is used. For example, when the first
internal electrode layer 11 and the second internal electrode layer
21 include phosphoric acid salt including Co and Li, it is
preferable that the solid electrolyte layer 30 includes
Li--Al--Ge--PO.sub.4-based material to which Co is added in
advance. In this case, it is possible to suppress solving of the
transition metal included in the electrode active material into the
electrolyte. When the first internal electrode layer 11 and the
second internal electrode layer 21 include phosphoric acid salt
including Li and a transition metal other than Co, it is preferable
that the solid electrolyte layer 30 includes
Li--Al--Ge--PO.sub.4-based material in which the transition metal
is added in advance.
[0017] At least, the first internal electrode layer 11 used as a
positive electrode includes a material having an olivine type
crystal structure, as an electrode active material. It is
preferable that the second internal electrode layer 21 also
includes the electrode active material. The electrode active
material is such as phosphoric acid salt including a transition
metal and lithium. The olivine type crystal structure is a crystal
of natural olivine. It is possible to identify the olivine type
crystal structure, by using X-ray diffraction.
[0018] For example, LiCoPO.sub.4 including Co may be used as a
typical example of the electrode active material having the olivine
type crystal structure. Other salts of phosphoric acid, in which Co
acting as a transition metal is replaced to another transition
metal in the above-mentioned chemical formula, may be used. A ratio
of Li or PO.sub.4 may fluctuate in accordance with a valence. It is
preferable that Co, Mn, Fe, Ni or the like is used as the
transition metal.
[0019] The electrode active material having the olivine type
crystal structure acts as a positive electrode active material in
the first internal electrode layer 11 acting as a positive
electrode. For example, when only the first internal electrode
layer 11 includes the electrode active material having the olivine
type crystal structure, the electrode active material acts as the
positive electrode active material. When the second internal
electrode layer 21 also includes an electrode active material
having the olivine type crystal structure, discharge capacity may
increase and an operation voltage may increase because of electric
discharge, in the second internal electrode layer 21 acting as a
negative electrode. The function mechanism is not completely clear.
However, the mechanism may be caused by partial solid-phase
formation together with the negative electrode active material.
[0020] When both the first internal electrode layer 11 and the
second internal electrode layer 21 include an electrode active
material having the olivine type crystal structure, the electrode
active material of each of the first internal electrode layer 11
and the second internal electrode layer 21 may have a common
transition metal. Alternatively, the a transition metal of the
electrode active material of the first internal electrode layer 11
may be different from that of the second internal electrode layer
21. The first internal electrode layer 11 and the second internal
electrode layer 21 may have only single type of transition metal.
The first internal electrode layer 11 and the second internal
electrode layer 21 may have two or more types of transition metal.
It is preferable that the first internal electrode layer 11 and the
second internal electrode layer 21 have a common transition metal.
It is more preferable that the electrode active materials of the
both electrode layers have the same chemical composition. When the
first internal electrode layer 11 and the second internal electrode
layer 21 have a common transition metal or a common electrode
active material of the same composition, similarity between the
compositions of the both electrode layers increases. Therefore,
even if terminals of the all solid battery 100 are connected in a
positive/negative reversed state, the all solid battery 100 can be
actually used without malfunction, in accordance with the usage
purpose.
[0021] The second internal electrode layer 21 may include known
material as the negative electrode active material. When only one
of the electrode layers includes the negative electrode active
material, it is clarified that the one of the electrode layers acts
as a negative electrode and the other acts as a positive electrode.
When only one of the electrode layers includes the negative
electrode active material, it is preferable that the one of the
electrode layers is the second internal electrode layer 21. Both of
the electrode layers may include the known material as the negative
electrode active material. Conventional technology of secondary
batteries may be applied to the negative electrode active material.
For example, titanium oxide, lithium-titanium complex oxide,
lithium-titanium complex salt of phosphoric acid salt, a carbon, a
vanadium lithium phosphate.
[0022] In the forming process of the first internal electrode layer
11 and the second internal electrode layer 21, moreover,
oxide-based solid electrolyte material or a conductive material
(conductive auxiliary agent) such as a carbon material or a metal
material may be added. When the material is evenly dispersed into
water or organic solution together with binder or plasticizer,
paste for electrode layer is obtained. Pd, Ni, Cu, or Fe, or an
alloy thereof may be used as a metal of the conductive auxiliary
agent.
[0023] A main component of the first electric collector layer 12
and the second electric collector layer 22 is conductive
material.
[0024] FIG. 2 illustrates a schematic cross section of an all solid
battery 100a in which a plurality of cell units are stacked. The
all solid battery 100a has a multilayer chip 60 having a
rectangular parallelepiped shape. The all solid battery 100a has a
first external electrode 40a formed on a first end face of the
multilayer chip 60 and a second external electrode 40b formed on a
second end face facing with the first end face.
[0025] In four faces other than the two end faces of the multilayer
chip 60, two faces other than an upper face and a lower face of the
multilayer chip 60 in a stacking direction are referred to as side
faces. The first external electrodes 40a and the second external
electrode 40b extend to the upper face, the lower face and the two
side faces of the multilayer chip 60. However, the first external
electrode 40a and the second external electrode 40b are spaced from
each other.
[0026] In the following description, the same numeral is added to
each member that has the same composition range, the same thickness
range and the same particle distribution range as that of the all
solid battery 100. And, a detail explanation of the same member is
omitted.
[0027] In the all solid battery 100a, each of the first electric
collector layers 12 and each of the second electric collector
layers 22 are alternately stacked. Edges of the first electric
collector layers 12 are exposed to the first edge face of the
multilayer chip 60 but are not exposed to the second edge face of
the multilayer chip 60. Edges of the second electric collector
layers 22 are exposed to the second edge face of the multilayer
chip 60 but are not exposed to the first edge face. Thus, each of
the first electric collector layers 12 and each of the second
electric collector layers 22 are alternately conducted to the first
external electrode 40a and the second external electrode 40b.
[0028] The first internal electrode layer 11 is stacked on the
first electric collector layer 12. The solid electrolyte layer 30
is stacked on the first internal electrode layer 11. The solid
electrolyte layer 30 extends from the first external electrode 40a
to the second external electrode 40b. The second internal electrode
layer 21 is stacked on the solid electrolyte layer 30. The second
electric collector layer 22 is stacked on the second internal
electrode layer 21. Another second internal electrode layer 21 is
stacked on the second electric collector layer 22. Another solid
electrolyte layer 30 is stacked on the second internal electrode
layer 21. The solid electrolyte layer 30 extends from the first
external electrode 40a to the second external electrode 40b. The
first internal electrode layer 11 is stacked on the solid
electrolyte layer 30. In the all solid battery 100a, the stack
units are repeatedly stacked. Therefore, the all solid battery 100a
has a structure in which a plurality of cell units are stacked.
[0029] In the all solid battery 100 and the all solid battery 100a,
the composition of the Li-AL-M-PO.sub.4-based phosphoric acid salt
of the solid electrolyte layer 30 may fluctuate. In concrete, "M"
of the Li--Al-M-PO.sub.4-based phosphoric acid salt may diffuse
toward the first internal electrode layer 11 side and the second
internal electrode layer 21 side.
[0030] FIG. 3A to FIG. 3C illustrate schematic cross sectional view
of the solid electrolyte layer 30 and the first internal electrode
layer 11 adjacent to the solid electrolyte layer 30, and the second
internal electrode layer 21 adjacent to the solid electrolyte layer
30. For example, as illustrated in FIG. 3A, when "M" diffuses,
crystal grains 50 of MO.sub.2 may exist around the interface
between the solid electrolyte layer 30 and the first internal
electrode layer 11 and the interface between the solid electrolyte
layer 30 and the second internal electrode layer 21. In this case,
MO.sub.2 is not an ionic conductive material, an interface
resistance between the solid electrolyte layer 30 and the first
internal electrode layer 11 and an interface resistance between the
solid electrolyte layer 30 and the second internal electrode layer
21 may increase.
[0031] Next, as illustrated in FIG. 3B, there may be a case where
"M" of the Li--Al-M-PO.sub.4-based phosphoric acid salt excessively
diffuse, and the crystal grain 50 does not exist in the solid
electrolyte layer 30. In this case, the amount of M of the
Li--Al-M-PO.sub.4-based phosphoric acid salt becomes smaller, and
the composition may fluctuate. In this case, the ionic conductivity
of the solid electrolyte layer 30 may be degraded.
[0032] Therefore, the rate characteristic of the all solid battery
100 and the all solid battery 100a may be reduced, in both of the
cases of FIG. 3A and FIG. 3B.
[0033] The all solid battery 100 and the all solid battery 100a
have a structure for achieving high ionic conductivity. In
concrete, a segregation range of MO.sub.2 is unevenly distributed
in a center portion in the thickness direction of the solid
electrolyte layer 30. As illustrated in FIG. 3C, when the thickness
of the solid electrolyte layer 30 is expressed by "A", the
segregation range of MO.sub.2 is unevenly distributed from the
center in the thickness of the solid electrolyte layer 30 to 0.4 A
downward and to 0.4 A upward. It is preferable that the segregation
range of MO.sub.2 is narrow. For example, it is preferable that the
segregation range of MO.sub.2 is unevenly distributed from the
center in the thickness of the solid electrolyte layer 30 to 0.2 A
downward and to 0.2 A upward. It is more preferable that the
segregation range of MO.sub.2 is unevenly distributed from the
center in the thickness of the solid electrolyte layer 30 to 0.1 A
downward and to 0.1 A upward. It is still more preferable that the
segregation range of MO.sub.2 is unevenly distributed from the
center in the thickness of the solid electrolyte layer 30 to 0.025
A downward and to 0.025 A upward. When MO.sub.2 is segregated,
MO.sub.2 does not exist in a structure of Li--Al-M-PO.sub.4 but
independently exits in the structure of MO.sub.2 (crystal grains of
MO.sub.2) in which "P" does not exist. The segregation range of
MO.sub.2 is a range in which an existence ratio of MO.sub.2 is 5%
or more with respect to the Li--Al-M-PO.sub.4-based base material.
When the segregation range of MO.sub.2 is unevenly distributed in
the center portion, the segregation range of MO.sub.2 exists in
only the center portion and does not exist other region.
[0034] It is possible to measure the segregation range of MO.sub.2
by measuring an area where only "M" and O (oxygen) exist, by a
ToF-SIMS and a SEM-EDS mapping analysis. For example, as
illustrated in FIG. 4, the solid electrolyte layer 30 is divided
into 20 rectangular strip shapes having a thickness of 0.05 A when
the thickness of the solid electrolyte layer 30 is "A". Each area
where only "M" and O (oxygen) exist is measured in each rectangular
strip shape. Thus, it is possible to calculate an area ratio of
MO.sub.2 with respect to the Li--Al-M-PO.sub.4-based base
material.
[0035] In the embodiment the segregation range of MO.sub.2 is
unevenly distributed in a center portion of the solid electrolyte
layer 30 in the thickness direction. Thus, it is possible to reduce
the interface resistance between the solid electrolyte layer 30 and
the first internal electrode layer 11 and the interface resistance
between the solid electrolyte layer 30 and the second electrode
layer 21. When the MO.sub.2 exists in the solid electrolyte layer
30, lack of M in the Li--Al-M-PO.sub.4 is suppressed. And the
composition changing is suppressed. It is therefore possible to
secure the ionic conductivity of the solid electrolyte layer 30.
Accordingly, it is possible to achieve high ionic conductivity.
[0036] When the crystal grain diameter of the crystal grain 50 not
having ionic conductivity is large, ionic conductive paths are
hardly secured. It is therefore preferable that an average crystal
grain diameter of the crystal grains 50 has an upper limit. For
example, it is preferable that the average crystal grain diameter
of the crystal grains 50 is 5 .mu.m or less. It is more preferable
that the average crystal grain diameter is 2 .mu.m or less. On the
other hand, when the crystal grain diameter of the crystal grains
50 is small, probability of prevention of ion movement gets larger.
It is therefore preferable that the average crystal grain diameter
of the crystal grains 50 has a lower limit. For example, it is
preferable that the average crystal grain diameter of the crystal
grains 50 is 0.2 .mu.m or more. It is more preferable that the
average crystal grain diameter is 0.5 .mu.m or more.
[0037] When the thickness of the solid electrolyte layer 30 is
small, the ionic conductive path may be short. It is therefore
preferable that the thickness of the solid electrolyte layer 30 has
an upper limit. For example, the thickness of the solid electrolyte
layer 30 is, 30 .mu.m or less, 15 .mu.m or less, or 10 .mu.m or
less. On the other hand, when the thickness of the solid
electrolyte layer 30 is small, short between electrodes may occur.
It is therefore preferable that the thickness of the solid
electrolyte layer 30 is 2 .mu.m or more. It is preferable that the
average grain diameter of the crystal grains 50 is within "the
thickness of the solid electrolyte layer 30.times.0.1.+-.20%".
[0038] FIG. 5 illustrates a flowchart of the manufacturing method
of the all solid battery 100a.
[0039] (Making process of ceramic material powder) Powder of
oxide-based solid electrolyte for the solid electrolyte layer 30 is
made. In concrete, Li--Al-M-PO.sub.4-based phosphoric acid salt is
made. For example, it is possible to make the solid electrolyte
powder, by mixing raw material and additives and using solid phase
synthesis method or the like. The resulting powder is subjected to
dry grinding. Thus, a grain diameter of the resulting power is
adjusted to a desired one. For example, it is possible to adjust
the grain diameter to the desired diameter with use of planetary
ball mill using ZrO.sub.2 ball of 5 mm .PHI..
[0040] The additive includes sintering assistant. The sintering
assistant includes one or more of glass components such as
Li--B--O-based compound, Li--Si--O-based compound, Li--C--O-based
compound, Li--S--O-based compound and Li--P--O-based compound.
[0041] (Making process of green sheet) The resulting powder is
evenly dispersed into aqueous solvent or organic solvent together
with a binding agent, a dispersing agent, a plasticizer and so on.
The resulting powder is subjected wet crushing. And solid
electrolyte slurry having a desired particle diameter is obtained.
In this case, a bead mill, a wet jet mill, a kneader, a high
pressure homogenizer or the like may be used. It is preferable that
the bead mill is used because adjusting of particle size
distribution and dispersion are performed at the same time. A
binder is added to the resulting solid electrolyte slurry. Thus,
solid electrolyte paste is obtained. The solid electrolyte paste is
painted. Thus, a green sheet is obtained. The painting method is
not limited. For example, a slot die method, a reverse coat method,
a gravure coat method, a bar coat method, a doctor blade method or
the like may be used. It is possible to measure the particle size
distribution after the wet-crushing, by using a laser diffraction
measurement device using a laser diffraction scattering method.
[0042] In the making of the green sheet, the crystal grains 50 of
MO.sub.2 are arranged in the center portion of the green sheet in
the thickness direction. For example, the crystal grains 50 having
the average particle diameter of 0.2 .mu.m or more and 5 .mu.m or
less. For example, the crystal grains 50 are arranged in only a
range from the center in the thickness of the green sheet to 0.4 A
downward and to 0.4 A upward, when the thickness of the green sheet
is expressed by "A". It is preferable that the range in the
thickness direction is narrow. For example, it is preferable that
the range is a range from the center in the thickness of the green
sheet to 0.2 A downward and to 0.2 A upward. It is more preferable
that the range is a range from the center in the thickness of the
green sheet to 0.1 A downward and to 0.1 A upward. It is still more
preferable that the range is a range from the center in the
thickness of the green sheet to 0.025 A downward and to 0.025 A
upward
[0043] (Making process of paste for internal electrode) Next, paste
for internal electrode is made in order to make the first internal
electrode layer 11 and the second internal electrode layer 21. For
example, a conductive auxiliary agent, an active material, a solid
electrolyte material, a binder, a plasticizer and so on are evenly
dispersed into water or organic solvent. Thus, paste for internal
electrode layer is obtained. The above-mentioned solid electrolyte
paste may be used as the solid electrolyte material. Pd, Ni, Cu,
Fe, or alloy thereof, or a carbon material may be used as the
conductive auxiliary agent. When the composition of the first
internal electrode layer 11 is different from that of the second
internal electrode layer 21, paste for internal electrode used for
the first internal electrode layer 11 and another paste for
internal electrode used for the second internal electrode layer 21
may be individually made.
[0044] (Making process of paste for electric collector) Next, paste
for electric collector is made in order to make the first electric
collector layer 12 and the second electric collector layer 22. It
is possible to make the paste for electric collector, by evenly
dispersing Pd powder, carbon black, board-shaped graphite carbon, a
binder, dispersant, plasticizer and so on into water or organic
solvent.
[0045] (Stacking process) Paste 52 for internal electrode is
printed on one face of a green sheet 51 as illustrated in FIG. 6.
Paste 53 for electric collector is printed on the paste 52 for
electrode layer. And, another paste 52 for internal electrode is
printed on the paste 53 for electric collector. A reverse pattern
54 is printed on a part of the green sheet 51 where neither the
paste 52 for electrode layer nor the paste 53 for electric
collector is printed. A material of the reverse pattern 54 may be
the same as that of the green sheet 51. The green sheets 51 after
printing are stacked so that each of the green sheets 51 is
alternately shifted to each other. Thus, a multilayer structure is
obtained. In this case, the multilayer structure is formed so that
each of the combinations of the paste 52 for internal electrode and
the paste 53 for electric collector is alternately exposed to each
of two end faces, in the multilayer structure,
[0046] (Firing process) Next, the multilayer structure is fired. In
the firing process, it is preferable that a maximum temperature is
400 degrees C. to 1000 degrees C. in oxidizing atmosphere or
non-oxidizing atmosphere. It is more preferable that that maximum
temperature is 500 degrees C. to 900 degrees C. In order to
sufficiently remove the binder until the maximum temperature, a
process for keeping a temperature lower than the maximum
temperature in oxidizing atmosphere may be performed. It is
preferable that the firing is performed in the lowest possible
temperature, from a viewpoint of reduction of the process cost.
After the firing, a re-oxidizing process may be performed. In this
manner, the multilayer chip 60 is formed.
[0047] After that, metal paste is applied to the two end faces of
the multilayer chip 60. And, the metal paste is fired. Thus, the
first external electrode 40a and the second external electrode 40b
are formed. Alternatively, the multilayer chip 60 may be put in a
dedicated tool so that the first external electrode 40a is spaced
from the second external electrode 40b on the upper face, the lower
face and the two side faces connected to the two end faces. And,
electrodes may be formed by a sputtering. The first external
electrode 40a and the second external electrode 40b may be formed
by plating on the formed electrodes.
[0048] In the embodiment, the green sheet 51 includes MO.sub.2
particles. The firing condition of the firing process is adjusted.
Thus, the segregation range of MO.sub.2 is unevenly distributed
from the center in the thickness of the solid electrolyte layer 30
to 0.4 A downward and to 0.4 A upward, when the thickness of the
solid electrolyte layer 30 is expressed by "A". In this case, it is
possible to reduce the interface resistance between the solid
electrolyte layer 30 and the first internal electrode layer 11 and
the interface resistance between the solid electrolyte layer 30 and
the second internal electrode layer 21. When the MO.sub.2 exists in
the solid electrolyte layer 30, lack of M in the Li--Al-M-PO.sub.4
is suppressed. And the composition changing is suppressed. It is
therefore possible to secure the ionic conductivity of the solid
electrolyte layer 30. Accordingly, it is possible to achieve high
ionic conductivity. When the green sheet 51 excessively includes
MO.sub.2 particles, lack of "M" in the Li--Al-M-PO.sub.4 is
suppressed even if the firing process is performed at a high
temperature (for example 600 degrees C. or more). That is, the
firing process at a high temperature can be performed. In this
case, sintering characteristic of the solid electrolyte layer 30 is
favorable, and high ionic conductivity is achieved.
EXAMPLES
[0049] The all solid batteries in accordance with the embodiment
were made and the property was measured.
[0050] (Examples 1 to 4 and Comparative examples 1 to 3)
Co.sub.3O.sub.4, Li.sub.2CO.sub.3, dihydrogen phosphate ammonium,
Al.sub.2O.sub.3, GeO.sub.2 were mixed and were used as solid
electrolyte material powder. From the solid electrolyte material
powder, Li.sub.1.3Al.sub.0.3Ge.sub.1.7(PO.sub.4).sub.3 including a
predetermined amount of Co was made by a solid phase synthesizing.
The resulting power was crushed. Thus, solid electrolyte slurry was
made. Solid electrolyte paste was obtained by adding a binder to
the resulting slurry. And, solid electrolyte green sheet was made.
Li.sub.1.3Al.sub.0.3Ti.sub.1.7(PO.sub.4).sub.3 including a
predetermined amount of LiCoPO.sub.4 and Co was synthesized by a
solid phase synthesizing as well as the above-mentioned oxide.
Thus, the paste for internal electrode was made.
[0051] Paste for internal electrode having a thickness of 2 .mu.m
was printed on the solid electrolyte green sheet, with use of a
screen having a predetermined pattern. And, paste for electric
collector was printed on the paste for internal electrode. And,
paste for internal electrode having a thickness of 2 .mu.m was
printed on the paste for electric collector. 11 numbers of the
green sheets after the printing were stacked so that each of the
electrodes is alternately shifted to right and left. Cover sheets
having an average thickness of 30 .mu.m in which solid electrolyte
green sheets were stacked were adhered to an upper face and a lower
face of the multilayer structure of the stacked green sheets after
the printing. The cover sheets were crimped to the multilayer
structure by a heating pressurizing press. The resulting multilayer
structure was stamped into a predetermined size by a dicer.
[0052] The binder was removed from the chip after cutting by a
thermal treatment in a temperature range of 300 degrees C. to 500
degrees C. After that, the chip was sintered by a thermal treatment
of 900 degrees C. or less. Thus, a sintered structure was made. A
cross section of the sintered structure was observed with use of
SEM. The thickness of the solid electrolyte layer 30 was measured.
With respect to the examples 1 and 2 and the comparative examples 1
and 2, the thickness of the solid electrolyte layer 30 was 10
.mu.m. The thickness of the solid electrolyte layer 30 was 20
.mu.m, with respect to the examples 3 and 4 and the comparative
example 3.
[0053] An area where only Ge and O (oxygen) exist was measured by a
ToF-SIMS and a SEM-EDS mapping analysis. Thus, the segregation
range of MO.sub.2 was measured. In concrete, as illustrated in FIG.
4, the solid electrolyte layer 30 was divided into 20 rectangular
strip shapes having a thickness of 0.05 A when the thickness of the
solid electrolyte layer 30 is expressed by "A". With respect to
each of rectangular strip shapes, each area ratio of MO.sub.2 with
respect to the Li--Al-M-PO.sub.4-based phosphoric acid salt base
material was calculated. A range in which an existence ratio of
MO.sub.2 is 5% or more with respect to the Li--Al-M-PO.sub.4-based
base material was defined as the segregation range. Table 1 shows
the results.
[0054] Next, with respect to the examples 1 to 4 and the
comparative examples 1 to 3, ionic conductivity was measured. As a
measuring apparatus, a frequency response analyzer 1255B made by
Solartron was used. The temperature was 25 degrees C. Measured
frequency range was 500000 Hz to 0.1 Hz. When the measured ionic
conductivity was 5.times.10.sup.-5 S/cm or more, the ionic
conductivity of the base material was determined as good
".largecircle.". When the ionic conductivity was less than
5.times.10.sup.-5 S/cm, the ionic conductivity of the base material
was determined as bad ".times.".
TABLE-US-00001 TABLE 1 IONIC GeO.sub.2 AMOUNT OF CONDUCTIVITY
THICKNESS SEGREGATION GeO.sub.2 NEAR OF BASE TOTAL (.mu.m) RANGE
INTERFACE MATERIAL EVALUATION EXAMPLE 1 10 0.25A EXAMPLE 2 10 0.05A
EXAMPLE 3 20 0.25A EXAMPLE 4 20 0.025A COMPARATIVE 10 0.45A .times.
.times. EXAMPLE 1 COMPARATIVE 10 0 .times. .times. EXAMPLE 2
COMPARATIVE 20 0.45A .times. .times. EXAMPLE 3 COMPARATIVE 20 0
.times. .times. EXAMPLE 4
[0055] In the example 1, when the thickness of the solid
electrolyte layer 30 is expressed by "A", the segregation range of
MO.sub.2 was unevenly distributed from the center in the thickness
of the solid electrolyte layer 30 to 0.25 A downward and to 0.25 A
upward. In the example 2, the segregation range of MO.sub.2 was
unevenly distributed from the center in the thickness of the solid
electrolyte layer 30 to 0.05 A downward and to 0.05 A upward. In
the example 3, the segregation range of MO.sub.2 was unevenly
distributed from the center in the thickness of the solid
electrolyte layer 30 to 0.25 A downward and to 0.25 A upward. In
the example 4, the segregation range of MO.sub.2 was unevenly
distributed from the center in the thickness of the solid
electrolyte layer 30 to 0.025 A downward and to 0.025 A upward. In
the comparative example 1, the segregation range of MO.sub.2 was
unevenly distributed from the center in the thickness of the solid
electrolyte layer 30 to 0.45 A downward and to 0.45 A upward. In
the comparative example 2, MO.sub.2 was not unevenly distributed.
In the comparative example 3, the segregation range of MO.sub.2 was
unevenly distributed from the center in the thickness of the solid
electrolyte layer 30 to 0.45 A downward and to 0.45 A upward. In
the comparative example 4, MO.sub.2 was not unevenly
distributed.
[0056] When the total of the segregation range of MO.sub.2 is 0.8 A
or less, the amount of GeO.sub.2 near the interface of Table 1 was
determined as good ".largecircle.". When the total of the
segregation range of MO.sub.2 is more than 0.8 A, the amount of
GeO.sub.2 near the interface of Table 1 was determined as bad
".times.". In the comparative examples 2 and 4, GeO.sub.2 was not
unevenly distributed. Therefore, the amount of GeO.sub.2 near the
interface of Table 1 was determined as good ".largecircle.". When
the amount of GeO.sub.2 near the interface was determined as good,
ion conductive paths near the interface can be secured. On the
other hand, the amount of GeO.sub.2 near the interface was
determined as bad, the number of ion conductive paths near the
interface is small.
[0057] With respect to the examples 1 to 4 and the comparative
examples 1 and 3, the ionic conductivity of the base material was
determined as good ".largecircle.". It is thought that this was
because the crystal grains of GeO.sub.2 existed in the solid
electrolyte layers 30, the reduction amount of Ge from the
Li--Al--Ge--PO.sub.4-based phosphoric acid salt was small, and the
ionic conductivity was secured. On the other hand, with respect to
the comparative examples 2 and 3, the ionic conductivity of the
base material was determined as bad ".times.". It is thought that
this was because GeO.sub.2 did not exist in the solid electrolyte
layers 30, the reduction amount of Ge from the
Li--Al--Ge--PO.sub.4-based phosphoric acid salt base material was
large, and the ionic conductivity was degraded.
[0058] When the amount of GeO.sub.2 near the interface and the
ionic conductivity of the base material were determined as good,
the total evaluation of Table 1 was determined as good
".largecircle.". When at least one of the amount of GeO.sub.2 near
the interface and the ionic conductivity of the base material was
determined as bad, the total evaluation was determined as bad
".times.".
[0059] Although the embodiments of the present invention have been
described in detail, it is to be understood that the various
change, substitutions, and alterations could be made hereto without
departing from the spirit and scope of the invention.
* * * * *